Police have released footage of the moment officers opened fire and shot dead a teenage girl in a custody waiting room.

Kristiana Coignard, 17, died after being shot four times at Longview police station in Texas last Thursday.

Her death has sparked outrage around the globe and her family have questioned why officers opened fire on the teenager, who suffered from mental health problems.

Police chiefs have now released video of Kristiana lunging at one officer as they seek to justify the use of the firearms against her. Police say she had pulled a butcher's knife from her waistband when she sprung towards them.

The video shows a confrontation escalate between the 17-year-old an Officer Glen Derr and a scuffle breaks out between them as he attempts to restrain her. Police claim she had written 'I have a gun' on her hand and had shown it to the officer.

Officer Derr is then joined by two colleagues - Gene Duffie and Grace Bagley - who corner the teenage girl before she leaps towards one of them as he points a gun in her direction. The video then cuts to show her lying on the ground.

Outrage: Kristiana Coignard's family have questioned why officers opened fire on the teenager, who suffered mental health problems (Image: Facebook)

Police say Duffie fired a Taser which failed to stop her and she was then shot by his two other colleagues.